Mobile scaffolding

ABSTRACT

There is disclosed a mobile scaffolding which is powered by self contained electrical storage batteries. The electric drive is mechanically linked to the lift mechanism of the scaffolding by mechanical means comprising screw means and a mating nut means interconnected by rolling means to provide a high efficiency coupling. The lift mechanism employs very compact spring means which is biased to extend the lift mechanism from its contracted position to provide a force that supplements the electric drive when the mechanism has the most unfavorable lever moment for extension of the scaffolding. The unit has a self contained power means for mobility and a self contained directional control means with remote control means whereby the entire unit can be controlled from the scaffolding platform with a single lever that actuates the lift, drive and steering motors.

United States Patent [1 91 Wehmeyer June 18, 1974 MOBILE SCAFFOLDING[76] Inventor: Donald T. Wehmeyer, 276

Mountain Cir., Fountain Valley, Calif. 94517 22 Filed: Aug. 21, 1972 21Appl. No.: 282,157

Primary Examiner-Reinaldo P. Machado Attorney, Agent, or Firm-Robert E.Strauss [5 7] ABSTRACT There is disclosed a mobile scaffolding which ispowered by self contained electrical storage batteries. The electricdrive is mechanically linked to the lift mechanism of the scaffolding bymechanical means comprising screw means and a mating nut meansinterconnected by rolling means to provide a high efficiency coupling.The lift mechanism employs very compact spring means which is biased toextend the lift mechanism from its contracted position to provide aforce that supplements the electric drive when the mechanism has themost unfavorable lever moment for ex tension of the scaffolding. Theunit has a self contained power means for mobility and a self containeddirectional control means with remote control means whereby the entireunit can be controlled from the scaffolding platform with a single leverthat actuates the lift, drive and steering motors.

17 Claims, 7 Drawing Figures PMENTEnJun 18 m4 sum 1 or 3 FIGURE 4 MOBILESCAFFOLDING DESCRIPTION OF THE INVENTION This invention relates tomobile scaffolding and, in particular, to a mobile unit having anelectric drive and a mechanical lift mechanism.

The construction industry, particularly that of tilt up wallconstruction employs scaffolding to a large extent for installation ofceilings and overhead utility facilities. This construction is usedlargely for warehouse and industrial building construction. Thefoundation and floor are generally poured concrete and the walls areformed as concrete panels which are cast on the floor and are thentilted upright and secured in place. These walls can be from about 8 to30 feet in height. Generally, all the utility facilities, electricalwiring or water or gas plumbing, etc., .are installed overhead, directlybeneath the roof.

Fixed or immobile scaffolding has been used to support workmen near theroof, however, workmen are needed at many different locations under theroof and the construction of fixed scaffolding at each of theselocations is time consuming and costly.. Mobile scaffolding which can bemoved about the building without dismantling has been used. Thisscaffolding comprises a mobile base with a work platform that can beelevated by jacks carried by the unit. These jacks have, withoutexception, been hydraulically actuated and generally have been poweredby a gasoline engine that is mounted on the unit. Gasoline engines areobjectionable for indoor work and require a substantial ventilation ofthe building when in use. While electric motors would be more desirableas a power source, their use has been limited by the inefficiency of thehydraulic mechanism used with the conventional mobile scaffold-Mechanical lifting mechanisms, however, have not been used for thisservice because of the large lifting force that is required during theinitial actuation of the lift when the lift mechanism provides the leastfavorable lever arm for the lifting force. Consequently, the direct useof a mechanical drive lift mechansim has necessitated a compromise inlift design, e.g., either the scaffolding must be too high in thecollapsed position or it fails to extend as high as desirable.

An extremely efficient mechanical drive means for use in the lift unitis a screw with mating screw engagement means having rolling contactwith the screw. The screw means can be combined with electric motivepower means in a highly efficient, portable or mobile scaffolding unithaving a minimum collapsed height and maximum extended height. I havefound that such a mechanical drive mechansim can be used with a portablescaffolding device provided that compact resilient means are provided tobias against the platform or any of the members of the extendibleassembly linking the platform to the base when the platform is in itsretracted position. The compact resilient means comprises at least onemassive compression spring which is coaxially placed about the liftscrew so that it is compressed when the platform is collapsed and isoperative to release its stored force to supplement the lift power meanswhen the platform is extended.

The mobile scaffolding of this invention comprises: a base, wheelscarried thereon, electric power means linked to at least one of thewheels to provide mobility to the base, directional control means topivot at least one of the wheels and provide steering of the base, aplatform, an extendible assembly mechanically interconnecting saidplatform and base and comprising at least one pair of arm members joinedtogether in a pivotable connection at an intermediate point of theirlength, platform attachment means securing a pair of free ends of theextendible assembly to the platform and base attachment means securingthe free ends of the opposite end of the assembly to the base, whilepermitting the sliding engagement of at least one of either or both ofsaid pairs of free ends with its respective platform or base, lift meansoperatively attached to at least one end of the extendible assemblycomprising screw means transversely positioned to the direction ofextension of the assembly, screw engagement means cooperative therewith,electrical lift motor means, interconnecting means linking said motor inrotational driving connection to one of said screw and screw engagingmeans to one of said pair of free ends whereby rotational movement ofsaid motor effects extension and retraction of the assembly, andresilient means coaxial with the screw means and operative to engage theextendible assembly in its retracted position and to resiliently urgemovement of said assembly from its retracted position whereby the forcestored in the resilient means by retraction of the assembly is availablefor supplementing the force of said electric lift motor means to extendthe assembly through the positions having the most disadvantageous levermoments. In its preferred embodiments, the scaffolding has remotecontrol means carried on the platform to control the actuation of thelift mechanism and the movement of the unit about the building. Theentire operation of the unit can be controlled by a single hand controlthat actuates switches in the respective circuits for the drive powermeans, the directional control power means or the lift motor means.

The invention will now be described with reference to the FIGURES, ofwhich:

FIG. 1 illustrates the mobile scaffolding unit in its most extendedposition;

FIG. 2 is a plan view of the base of the unit; FIG. 3 is a sectionalview along the line 3-3 of FIG. 2;

FIG. 4 illustrates the slidable connection of the extendible assembly;

FIG. 5 illustrates the electrical circuit of the unit; and

FIGS. 6 and 7 illustrate the hand control of the unit.

Referring now to FIG. 1, the mobile scaffolding unit comprises a base10, a platform 20 and an extendible assembly 30 mechanicallyinterlinking the platform and the base.

Base 10 has a protective cover 12 with sidewalls. The unit has a pair ofrear wheels 14 and a pair of forward wheels 16. The rear of base 10 iscovered by a plurality of cover plates 18. The forward pair of wheels 16are steerable and are mounted on base 10 with means permitting theiraxes to be turned to the right or left of the base.

The platform 20 has a floor 21 with a protective railing 22 about itsperiphery and an open section for access at its rear end. If desired,the railing can fold away from the platform or a gate can be furnishedfor the open section. At its front end, the platform preferably carriesa control console or pedestal 9 which supports an instrument and controlbox 24 for operation of the unit.

The extendible assembly 30 comprises at least one and, preferably, twopairs of arm members 31, 32, 33 and 34 which are pivotablyinterconnected at points intermediate their lengths, at hubs 35 and 36.For maximum stability, these pairs of arm members are duplicated at eachside of the scaffolding unit and are identified by common numbers. Eachassembly has one pair of its free ends, e.g., the upper ends of armmembers 31 and 32, attached to the platform and, at its opposite end,has the free ends of its arm members, e.g., the lower ends of armmembers 33 and 34 attached to the base 10. The attachment means at thefront of the base can be bracket members 37 which are supported on theframe of the base. A similar pair of bracket members can be provided onthe forward edge of the undersurface of platform 20.

The extendible assemblies 30 are vertically extendible and, accordingly,at least one of each pair of free ends of the assemblies is attached toeither the base or platform by means permitting its sliding engagementtherewith. While the free ends of both arm members 31 and 32 canslidably attach to the platform and the free ends of both arm members 33and 34 can slidably attach to the base, it is preferred that only one ofeach of these pairs be slidably attached to its respective base orplatform. This is shown in FIG. 1 where the lower end of the arm members33 of each of the assemblies is slidably attached to the base 10. Theends of these members are secured to curved flange plates 38 and 37which extend through grooves 40 and 41 and into the housing of base 10.The upper ends of members 32 bear rollers which are free to move inchannels on the underside of the platform. The remaining member of eachpair of free ends is secured to its respective platform or base bybrackets.

All the power and drive mechanisms for the unit can be contained withinthe housing of base 10, including the electrical energy storage means,motive power means for propulsion of the unit, its directional controland extension of the platform.

FIGS. 2 and 3 illustrate the construction and assembly of base 10. Thebase is formed by a pair of longitudinal beams 50 and 51 that run thelength of the base. These can be formed of sheet metal welded to providean upright, open channel. Two transverse beams are provided; 52 at thefront of and 53 intermediate the lengths of the longitudinal beams. Asheet 67 also extends transversely across the base a short distancebehind beam 52 and has an offset pocket 68 at the midline of base 10.The front of base is covered by plate 54 while the rear portion iscovered by plates 18 which extend between beams 50 and 51. The plateshave a short lip that overhangs the inside wall of these beams to holdthem in place. A narrow plate, 55, is secured over the channel andprovides open slots 40 and 41 along each beam.

Cover plate 54 extends to about 12 inches of both edges of the unit. Theremainder of the top comprises a hinged cover 56 at each side of theunit as shown in FIG. 1. Beneath the hinged cover are compartments forthe control circuit components 57, battery charger 74 and the electricalbatteries 129 which are placed six at each side.

The longitudinal beams have apertures near their rear ends and supportoutboard brackets 58 in line with the apertures. The rear axles 59extend through the apertures and through a bearing support carried bybracket 58. A conventional differential 60 is supported on the midlineof the base 10 with its axles extending to universal joints 61 thatconnect to axles 59. Other means such as flexible couplings can also beused in lieu of the universal joints. The power drive to thedifferential comprises electric motor 62, a conventional direct currentmotor of suitable voltage, e.g., 6 to 42 volts, that is linked bysprockets and chain 63 to the differential input shaft.

The forward wheels 16 are mounted on axles having upright spindles thatare journaled at 64 by a sleeve carried at the outboard end of beam 52.A trailing arm 65 projects from the wheel spindle and is pivotablysecured to a tie rod 66. The inboard end of rod 66 is secured to shaft72 by a ball joint coupling 73. The steering motor and its mechanicallinkage are mounted at the front center of base 10. The motor 10 fitsinto the pocket or housing 68 in transverse sheet 67 and is supported bybracket 69 that is carried by beam 52. The shaft of motor 70 isconnected to gear box 71. Shaft 72 projects through gear box 71 and hasa mid section bearing screw threads which engage a mating nut in gearbox 71. The nut is secured to a pinion gear that is meshed with a wormgear which is connected to the motor shaft so that rotation of the motoreffects side to side movement of rod 66.

The lift assembly, as previously described, comprises two pairs ofinterconnected arms at each side of the unit. The arms are preferablyformed by welding together the edges of two channels to form a hollowbeam having the illustrated shape. The lower ends of arms 34 arepivotably secured on base 10 by brackets 37 which are secured to theforward ends of the longitudinal beams 50 and 51. The lower end of arm33 is secured to plates 38 and 39 which project into base 10 and aremounted therein in sliding engagement with wheels such as 75 that arecontained within channel beams 50 and S1 and that roll on the insidebottom of these channel beams.

FIG. 4 illustrates the construction of the lower end of the arms 33.Plates 38 and 39 are secured, preferably by welding to the oppositesides of the arms 33. The plates are bored at 76 and collar 77 is flttedinto each bore. The collar has an annular flange 78 which fits againstthe outer side of the plate and can be secured thereto by welding orother suitable means. A bronze bushing 79 is placed within collar 77.Mounted between the plates 38 and 39 is cylindrical block 80. This blockhas trunions 81 at each end and a central bore 82 to accomodate shaft83. The bosses 81 fit in bearing relationship to bushing 79. Bore 85 istapped transversely through block 80 and set screw 84 is provided tolock shaft 83 in the block after assembly of the elements. The wheels 75are similarly carried on shaft 83 with a bushing. Block 80 is bored at86 and and the end of shaft 87 is threaded into one end of clevis 64which is free to pivot with its opposite end having a bore for shaft 83.

Each of the shafts 87 bears screw means, threads 88, as shown in FIGS. 2and 3 for the right side shaft. These shafts lie within the channelbeams 50 or 51. Each shaft 87 projects through a gear housing 89 and aflange plate 99 which extends across the channel directly forward ofgear housing 88. The end of shaft 87 which is opposite block 80 projectsinto tubular member 90 and bears a collar 91 that is secured thereto bythreads, welding or the like. Tubular member 90 has an end plate whichis bored to receive shaft 87 in a sliding fit and which serves as a stopto collar 91. The opposite end of member 90 is open and bears annularcollar 92 about its outer periphery.

Resilient means comprising compression spring 93 is mounted about member90 and is biased between flange 99 and collar 92. The retraction of theextendible assembly into the position shown in FIG. 3 compressesresilient springs 93. The springs are selected so that the dead weightof the platform and extendible assembly is sufficient to compress thesprings, thereby insuring that in the event of failure of the liftmotor, the unit can still be retracted.

The gear housings 89 comprise conventional units wherein screw threads88 engage in rolling contact at a nut that is driven by a worm gear onshaft 98. While other gear drives could be used, the drive with rollingcontact is preferred for its high efficiency. A commercially availablegear drive that can be used for this is a ball screw .Iactuatordescribed in US. Pat. No. 3,178,958 and manufactured by the Duff-NortonCompany, North Carolina. The nut of this unit, which is driven by screwthreads on shaft 98 has a helical race for ball bearings to provide arecirculating, rolling contact with the threads on shaft 98. This geardrive is preferred for its high efficiency. Other gear drives, e.g., adirect worm gear be used, if desired. The shafts 98 are coupled throughflexible couplings 100 to shaft 101 that is mechanically linked by chain103 to electric motor 102. The outboard end of shaft 98 extends throughgear housing 89 and bears brake means 104. Any conventional brake meanscan be used, preferably the brake has a solenoid which is biased to lockthe brake and is unlocked by the application of a direct current voltageto the solenoid coil. The brake should also have manual means for itsrelease and at least one of shafts 98 is extended, as shown, so that acrank can be attached to the shaft to permit manual lowering of the liftplatform.

Resilient spring means 93 are effective throughout 1 the initialmovement of the arms of the extendible assemblies from their positionsshown in FIG. 3. The springs should be compressed against the assemblyduring translation of the arms through an are from their compressedposition, shown in FIG. 3. to an angle of about 45, preferably about 40to the axis of the screw shaft 87. The arms in the embodiment shown inFIG. 3 have an angle to this axis when in the compressed position ofabout 7. Consequently, the springs are under compression when the armsare at an inclined angle to the axis of shafts 87 of from 7 to 40. Otherembodi' ments can have varied minimum angles of inclination from 2 toabout however, with most embodiments, the maximum angle of about 45, forcompression of the springs would be applicable.

During the initial movement of the assemblies from their retractedposition, the vertical component of force applied to the assemblies fromthe motor l02and through gear housings 89 is at a minimum value. In theabsence of the springs, a considerable force would need to be exerted tolift even the unloaded platform because of the unfavorable lever momentprovided to the lift motor. Springs 93, however, elastically releasetheir stored force to supplement the force of motor 102 and permitsubstantially the entire force of motor 102 to be applied to lifting ofany load on platform 20.

The resilient spring means are coaxial with the screw means to form avery compact power unit. Placement of these compression springs in theindicated position avoids expanding the structure to any significantdegree and insures a minimum collapsed height to the unit.

As the extendible assemblies are advanced to full extension, shafts 87are moved forward in their channels 50 and 51. The position of theforward end of these shafts is shown by the broken lines in FIGS. 2 and3. The forward ends project past flanges 105 which are transverselypositioned in the channels and which have a central bore through whichthe shafts project.

In a typical embodiment of the portable scaffolding as illustratedherein, the unit has a lift capacity of 2,000 pounds with a lift motorof 3.25 horsepower, a drive motor of 2.25 horsepower and a steeringmotor of 0.5 horsepower, all at 36 volts. The unit has twelve six voltbatteries and has a useful work period of 10 hours continuous usebetween recharging cycles. This is sufficient for about 5 days of normaluse. The extendible height of the scaffolding platform 20 above thefloor surface is 20 feet and the collapsed or retracted height is 4.5feet. The unit has a maximum ground speed of 7 miles per hour and aminimum lift time of from 30 to 40 seconds at the rated capacity load of2,000 pounds.

The entire unit can be controlled with a single hand lever which ismounted in a control box 24. The control box is illustrated in FIG. 6and the control circuit for the unit, including that of the control box,is shown by FIG. 5. The circuit of the control box is shown at the leftof FIG. 5 within the box defined by the broken lines.

The control box 24 has a hinged cover panel 152 that supports a keyswitch 154 and a manual four pole, double throw selector switch 156. Thetwo throw positions of this switch are identified as Lift and Drive onFIG. 5. The cover is slotted at 158 and a T-bar handle 160 protrudesthrough this slot. The handle has a threaded shaft 162 that is turnedinto a tapped bore of tube 164. The latter tube is slidably mounted in alarger diameter tube 166, the base of which bears journal 168 that ismounted on and secured to shaft 170. Shaft 170 is the shaft extensionfrom the accelerator master switch, not shown. The shaft has a segmentgear mounted on it that drives a pinion gear which in turn rotates thewiper of potentiometer 174, shown in FIG. 5. The shaft also bears camswhich move the levers of each of switches 176 and 178 also shown in FIG.5. When the handle is pushed forward in slot 158 and pivots shaft 170,the cams of switch 176 are actuated. Depending upon the position ofselector switch 156, this will close the contacts to the up relay of thecontactor panel 132 or the forward relay of contactor panel 133. Whenthe handle is pulled back in slot 158, it pivots shaft 170 and actuatesthe cam of switch 178. Again, depending upon the position of selectorswitch 156, this either closes the contacts of the down relay of panel132 or the. contacts of the reverse relay of panel 133. The operation ofthese relays will be described in greater deail hereinafter.

A compression spring, not shown, is in tube 166 and seats againstjournal 168. The spring is biased against the lower end of tube 164 andthis tube is retained in tube 166 by pin 180 that extends from atransverse bore in tube 164 outwardly and into an inverted T- groove182. The spring urges the handle assembly of tube 164 and handle 160upwardly so that pin 180 seats in the upright leg of groove 182, therebylocking the handle assembly against rotation about its axis. When thehandle is depressed against the tension of the spring, it can then berotated left or right, the pin 180 following the horizontal legs of thegroove 182.

The upper end of tube 164 bears a bracket 184 to which are secured twonormally open microswitches 186 and 188. These switches have spring armswhich support rollers 190 and 192 that bear against the side of thecontrol box 150. A view of the bracket and switches appears in FlG. 7.As the handle 160 is rotated clockwise about its axis, the switch leverof switch 188 is moved into contact with its spring arm and is depressedagainst this arm sufficiently to close its contacts. Switch 188 actuatesthe relays of the steering motor 124 to cause the motor to turn theforward wheels towards the right. Switch 186 actuates other relays toreverse the current through motor 124 and turn the wheels to the left.

The steering motor 70 and its normally open relays 190, 191, 192 and 193are shown at the upper right of FIG. 5. The positive lead 130 isconnected to the coils of the relays and to the contacts of relay 193and 190 while negative lead 140 is connected to the contacts of relays191 and 192. When switch 186 is closed by clockwise rotation of handle160 and when selector switch 156 is in the Drive position, thecoils ofrelays 192 and 193 are grounded to the negative lead 140 throughnormally closed left limit switch 194. The limit switch is mounted onthe unit near gear box 71 so that when the wheels have turned themaximum degree the contacts of this switch are opened by engagement withthe left end of shaft 72 or by left tie rod 66. Closing of the contactsof relays 192 and 193 permits current to flow from lead 130 through therelay contacts, the windings of motor 70 to negative lead 140. When thewheels have turned the maximum degree to the left, the contacts of limitswitch 194 will be forced open, breaking the circuit to the relay coils.Closing of the contacts of microswitch 188 by counterclockwise movementof handle 160 will close the contacts of relays 190 and 191 and causecurrent to flow through relay 190, the windings of motor 70 in anopposite direction than previously described, the contacts of relay 191and through limit switch 195 whichch will open when the wheels haveturned the maximum degree to the right. which The control circuits forthe lift and drive motors are based on commercially available circuitcomponents which have silicon controlled rectifiers, SCRs. Each motorcontrol circuit employs a silicon controlled rectifier panel, acontactor pane] and a pulse monitoring trip card. Both motors arecontrolled with a single accelerator master switch, which as previouslymentioned is actuated by handle 160.

The silicon controlled rectifier circuit employs a SCR to provide apulsed input to the motor contacts at a frequency of 50 to 300 times persecond. The duration of the closed motor contact period is a fixed valuedetermined by the rate of charge of a fixed capacitor in the siliconcontrolled rectifier panel while the duration of the open motor contactperiod is variable and is determined by the rate of charge of acapacitor which isin series with a potentiometer in the acceleratormaster control circuit. The wiper of the potentiometer is mechanicallylinked to the accelerator control so that the resistance can be varied;high resistance limiting the current flow to charge the turn-oncapacitor and thereby limiting the frequency of on cycles to the motorand low resistance, conversely, increasing the number of on cycles andincreasing the duration of the on time to the motor. The potentiometer,previously mentioned, is shown at 174 in FIG. 5.

The motors operate on the average voltage supplied to them. A lowfrequency of on cycles is the same as a steady state low voltage so thatthe motors turn slowly and their speed increase with increasingfrequency of on cycles, i.e., increasing average voltage. Somerefinements of the circuit, as it is commercially available, includeplacing a diode across the motor terminals so that induced current canflow through the motor windings during the off cycles, greatlyincreasing the efficiency of the motor operation.

The components for the lift and drive motor control circuits areavailable from the General Electric Company and are described in detailin the General Electric publication RKE-lS 1, Static Control forElectric Vehicles. These components are illustrated in FIG. 5 in theintegrated circuit for the scaffolding unit.

The lift motor is shown at 102 and the drive motor at 62. The armaturecontacts of these motors are shown at 119 and 121 and 123 and 125 formotors 102 and 62 respectively. The field or stator contacts are and 116and 117 and 118. The terminals of the armatures and fields of the motorsare connected through magnetic contactor panels 132 and 133. Thesepanels each have three relays, two of which are opposite acting doublethrow relays and are identified as D and U on panel 132 and R and F onpanel 133. The connections to the switch contacts of these relays areshown while the relay actuating coils are omitted to simplify thedrawing.

The positive lead 130 from batteries 129 is connected, through circuitbreaker 131, to an armature contact of each motor, 119 and 123. Theother armature contact of the lift motor 102 is connected to thenormally open switch terminals of down relay D and up relay U in themagnetic contactor panel 132. The armature contact of motor 62 issimilarly connected to the normally open terminals of the reverse relayR and the forward relay F of the magnetic contactor panel 133. One ofthe stator contacts of each motor, 115 and 117, is connected to theswitch pole terminal of the up relay U and the forward relay F of itsrespective panel 132 or 133. The opposite stator contacts 116 and 118are connected to the switch pole terminal of the down relay D andreverse relay R of their respective panels 132 and 133. The normallyclosed terminals of the relays are commonly connected to terminal T2 oftheir respective SCR control circuit.

The circuit through the motor and its contactor panel is describedherein with regard to lift motor 102. The current flows from positivelead through the armature of the motor, the closed contacts of the uprelay U, to stator contacts 115, through the field of the motor 102 toline 181 through the normally closed contacts of the down relay D tocontact T2 of the SCR panel and, in a controlled pulsing, through SCRpanel to the negative contact of the panel. When the up and down relayswitches are reversed, the current flows through the armature, throughthe down relay D to stator contact 116, through the field of motor 102in an opposite direction to that previously described to line 181through the normally closed contacts of the up relay U.

The actuating coils for the relays of the magnetic contactor panels arenot shown, however, the connecting leads to these coils are shown inFIG. as line 110 from terminal 8 and line 111 from terminal 6 ofterminal connector'strip 134 which lead to the coils of the down relay Dand up relay U, respectively. The opposite terminals of the relay coilshave a common lead 112 which extends to terminal 13A of the terminalconnector strip 134.

The selector switch 156 connects switches 176 and 178 into the controlcircuit for the drive motor 62. With the selector switch in the liftposition, closing of switch 176 by moving lever 160 forward will permitcurrent to flow from the positive lead 130, through lead 113 and thelift up limit switch 198 to contact 6 of the terminal connector strip134. This contact is connected to the coil of the up relay U, theopposite terminal of which is connected to terminal 13A of terminalconnector strip 134. Lead 115 connects 13A to contact 5 of thesafetycard 136. Contact 5 of this card is internally connected to the negativeterminal 1 by a safety circuit which disconnects the internal connectionin the event that excessive voltage appears across terminals 2 and 3 ofthe card. Terminals 4 and 6 of the card are connected to the positivelead and are connected to an internal circuit which requires that theexternal circuit to terminal 5 be opened to reset the card in the eventthat the internal connection is opened by an overload condition.

When the hand control lever 160 is moved fully forward, the cam on shaft170 closes switch 109 and current flows to the coil of relay 1A of themagnetic contactor panel through lead 117 and terminal 45 of theterminal connector strip 134. The common connector on the normallyclosed terminals of the down and up relays is connected through relay 1Ato negative lead 139, bypassing lead 181 and the SCR control circuit andpermitting full voltage operation of the motor.

Whenever the lift motor circuit is actuated, current flows from terminal27 of terminal connector strip 134,

' through the coil 119 of the solenoid of brake 104, re-

leasing this brake.

The limit switches for the lift motor 102 are located on the unit sothat the up limit switch 198 is opened when the assembly is fullyextended and the down limit switch 197 is opened when the assembly isfully retracted.

While the preceding discussion has been directed to actuation andoperation of the lift motor in the up mode, the operation of the closelyrelated circuit to actuate the down mode and the related circuits toactuate the drive motor in forward and reverse are substantiallyidentical. The actuating switch for the drive motor comparable to 109 isnot illustrated; its employment, as well as switch 109 and the 1A relaybypass circuit for the lift motor, is optional.

The invention has been described with regard to the illustrated andpresently preferred mode of practice. It is not intended that thisspecific illustration be unduly limiting of the invention. Instead, itis intended that the invention be defined by the means and their obviousequivalents set forth in the following claims.

What is claimed is:

l. A mobile scaffolding machine having:

a platform;

a base, axle means carried thereon, wheels on said axle means wherebysaid scaffolding is mobile;

an extendible assembly mechanically interlinking said platform and baseand comprising at least one pair of arm members joined together in apivotable connection at an intermediate point of their length;

platform attachment means securing a pair of free ends of saidextendible assembly to said platform;

base attachment means securing the opposite pair of free ends of saidextendibleassembly to said base;

said attachment means including longitudinal channel means carried oneach of said platform and base and wheeled means engaged therein andcarried by at least one of each of the pairs of free ends of saidassembly to permit its sliding engagement with its respective platformor base;

lift means operatively attached to at least one end of said extendibleassembly comprising screw means positioned transversely to the directionof extension of said assembly, screw engagement means cooperativetherewith, electric lift motor means, interconnecting means linking saidmotor in rotational driving relationship to one of said screw and screwengagement means and means securing at least one of said pair of freeends at said one end of said extendible assembly to at least one of saidscrew and screw engagement means whereby rotational movement of saidmotor effects the extension and retraction of said assembly;

resilient means comprising compression coil spring means carried on saidscaffolding coaxially with said screw means to engage said extendibleassembly between its retracted position and a partially extendedposition having said arm members at an angle no greater than about 45degrees to the horizontal and to urge extension of said assembly fromsaid retracted position to said partially extended position whereby theforce stored in said resilient means by retraction of said assembly isavailable for supplementing the force of said motor means through thepositions of said assembly having the most disadvantageous lever momentsto said screw means.

2. The scaffolding machine of claim 1 wherein said base carries:electric power means, means linking said power means to at least one ofsaid wheels to drive said scaffolding, directional control power means,means linking said control power means to at leat one of said wheels tosteer said scaffolding, and a source of electrical energy with connectormeans to said electric power means.

3. The scaffolding machine of claim 1 wherein said extendible assemblycomprises two assemblies of arms located at each side thereof.

4. The scaffolding machine of claim 3 wherein each of the extendibleassemblies of arms comprises four arms pivotably interconnected.

5. The scaffolding machine of claim 4 wherein each of said platform andbase attachment means includes a set of fixed brackets at one end ofsaid scaffolding.

6. The scaffolding machine of claim wherein screw and screw engagementmeans are positioned at each side of the scaffolding base.

7. The mobile scaffolding machine of claim 1 wherein said screw meanscomprises at least one screw rod longitudinally carried by said basewith one end thereof secured to said one end of said extendible assemblyand the opposite end thereof extending to said interconnecting means,the latter comprising a rotating nut drive member engaged by said screwrod in a thread drive housing.

8. The mobile scaffolding machine of claim 7 wherein said free end ofsaid screw rod extends past said threaded drive housing and into slidingengagement with a tubular member having a flanged abutment and coxiallysupporting said compression coil spring means between said abutment andsaid threaded drive housing.

9. A mobile scaffolding machine comprising:

a rectangular mobile base with dirigible wheels;

a pair of spaced-apart parallel channel means located on opposite sidesof said base, each of said channel means having a pivot fixture locatedat one end thereof;

a separate dolly means reciprocally confined in each of said channelmeans;

a first screw rod having one end connected to one of said dolly meansand extending coasially therefrom in its associated channel means towardits pivot fixture;

a second screw rod having one end connected to the other of said dollymeans and extending coaxially therefrom in its associated channel meanstoward its pivot fixture;

a first thread drive housing fixedly mounted intermediately of one ofsaid channel means and having a rotating nut drive member engaging thethreads of said first screw rod;

a second thread drive housing fixedly mounted intermediately of theother of said channel means and having a rotating nut drive memberengaging the threads of said second screw rod;

drive means in each of said housing for rotating its drive nut member;

a rigid cross shaft interconnecting said drive means of said housingsfor simultaneous rotation thereof;

an electric drive motor drivingly connected to said cross shaft wheresaid dolly means can be simultaneously advanced and retracted relativeto their respective pivot fixtures;

a pair of vertically oriented scissor-type lift arms, one of said pairconnected between one of said dolly means and its pivot fixture and theother of said pair connected between the other of said dolly means andits pivot fixture whereby a work platform connected to said pair ofvertically oriented lift arms is raised and lowered as said dolly meansare simultaneously reciprocated in their associated channel means.

10. The mobile scaffolding machine as defined in claim 9 wherein acompression spring is coaxially mounted between each threaded drivehousing and the end of its screw rod extending therefrom toward itsassociated pivot fixture whereby said compression spring will becompressed as its associated dolly moves away from its pivot fixture.

11. The mobile scaffolding machine of claim 10 wherein said compressionsprings are operative only to bias their associated screw rods when saidscissor-type lift arms are between their most retracted position and apartially extended position having said arms at an angle no greater thanabout 45 degrees to the horizontal and to urge extension of said liftarms from their retracted position to said partially extended positionwhereby the force stored in said compression springs by retraction ofsaid lift arms is available for supplementing the force of said motorthrough the positions of said lift arms having the most disadvantageouslever moments to said screw rods.

12. The mobile scaffolding machine as defined in claim 9 wherein theelectric drive motor is a variable speed drive motor so the speed ofsimultaneous movement of said dolly means in their associated channelscan be controlled.

13. The mobile scaffolding machine defined in claim 12 wherein theelectric drive motor is a DC drive motor and its speed is controlledwith a control circuit employing a SCR operable to pulse the drive motorat different frequencies to selectively change its speed.

14. The mobile scaffolding machine defined in claim 13 wherein a controlcircuit is provided to change the pulse rate of the SCR, said controlcircuit having a manually operated device for changing the pulse rate ofthe SCR circuit.

15. The mobile scaffolding machine defined in claim 14 wherein themanually controlled device includes a lever means which includes areversing switch and a potentiometer whereby advancing the lever from aneu tral position in one direction will cause the motor to driveclockwise at a rate proportional to the displacement of said lever froma neutral position and the advance of said lever from said neutralposition in the other direction will cause said motor to rotate in acounter-clockwise manner proportional to the distance said lever ismoved from said neutral position.

16. The mobile scaffolding machine as defined in claim 15 wherein thelever means is mounted on the work platform whereby the ascent anddescent of the platform can be controlled directly therefrom.

17. The mobile scaffolding machine as defined in claim 15 wherein therectangular mobile base with dirigible wheels includes an electric drivemotor and the control circuit can be switched so the lever means can beutilized to control the movement of said mobile base in speed anddirection.

. UNITED STATES PATENT ()fFICE CERTIFICATE OF CORRECTI N 3,817,346 gJune 18, 1974 DONALD 'r.- WEHMEYER Patent No.-

Inventofls) It is certified that error appears in the above-identifiedpatent and that said Letters Patent are hereby corrected as shown below:

Ch'ang'e inve ntor 's" address from a "276 Mountain Cit. Fountain y: w?to -276 Mo'untaire Cir. Clayton, Callf 2. 51111; v

signed. and 'eaiea this "7t h' day-January 1975.

Attestr v McCOY M. GIBSON JR. c. MARS HALL DANN Attesting OfficerComissioner' 6f Patents y FORM Po-mso (10.59)

1. A mobile scaffolding machine having: a platform; a base, axle meanscarried thereon, wheels on said axle means whereby said scaffolding ismobile; an extendible assembly mechanically interlinking said platformand base and comprising at least one pair of arm members joined togetherin a pivotable connection at an intermediate point of their length;platform attachment means securing a pair of free ends of saidextendible assembly to said platform; base attachment means securing theopposite pair of free ends of said extendible assembly to said base;said attachment means including longitudinal channel means carried oneach of said platform and base and wheeled means engaged therein andcarried by at least one of each of the pairs of free ends of saidassembly to permit its sliding engagement with its respective platformor base; lift means operatively attached to at least one end of saidextendible assembly comprising screw means positioned transversely tothe direction of extension of said assembly, screw engagement meanscooperative therewith, electric lift motor means, interconnecting meanslinking said motor in rotational driving relationship to one of saidscrew and screw engagement means and means securing at least one of saidpair of free ends at said one end of said extendible assembly to atleast one of said screw and screw engagement means whereby rotationalmovement of said motor effects the extension and retraction of saidassembly; resilient means comprising compression coil spring meanscarried on said scaffolding coaxially with said screw means to engagesaid extendible assembly between its retracted position and a partiallyextended position having said arm members at an angle no greater thanabout 45 degrees to the horizontal and to urge extension of saidassembly from said retracted position to said partially extendedposition whereby the force stored in said resilient means by retractionof said assembly is available for supplementing the force of said motormeans through the positions of said assembly having the mostdisadvantageous lever moments to said screw means.
 2. The scaffoldingmachine of claim 1 wherein said base carries: electric power means,means linking said power means to at least one of said wheels to drivesaid scaffolding, directional control power means, means linking saidcontrol power means to at leat one of said wheels to steer saidscaffolding, and a source of electrical energy with connector means tosaid electric power means.
 3. The scaffolding machine of claim 1 whereinsaid extendible assembly comprises two assemblies of arms located ateach side thereof.
 4. The scaffolding machine of claim 3 wherein each ofthe extendible assemblies of arms comprises four arms pivotablyinterconnected.
 5. The scaffolding machine of claim 4 wherein each ofsaid platform and base attachment means includes a set of fixed bracketsat one end of said scaffolding.
 6. The scaffolding machine of claim 5wherein screw and screw engagement means are positioned at each side ofthe scaffolding base.
 7. The mobile scaffolding machine of claim 1wherein said screw means comprises at least one screw rod longitudinallycarried by said base with one end thereof secured to said one end ofsaid extendible assembly and the oPposite end thereof extending to saidinterconnecting means, the latter comprising a rotating nut drive memberengaged by said screw rod in a thread drive housing.
 8. The mobilescaffolding machine of claim 7 wherein said free end of said screw rodextends past said threaded drive housing and into sliding engagementwith a tubular member having a flanged abutment and coxially supportingsaid compression coil spring means between said abutment and saidthreaded drive housing.
 9. A mobile scaffolding machine comprising: arectangular mobile base with dirigible wheels; a pair of spaced-apartparallel channel means located on opposite sides of said base, each ofsaid channel means having a pivot fixture located at one end thereof; aseparate dolly means reciprocally confined in each of said channelmeans; a first screw rod having one end connected to one of said dollymeans and extending coasially therefrom in its associated channel meanstoward its pivot fixture; a second screw rod having one end connected tothe other of said dolly means and extending coaxially therefrom in itsassociated channel means toward its pivot fixture; a first thread drivehousing fixedly mounted intermediately of one of said channel means andhaving a rotating nut drive member engaging the threads of said firstscrew rod; a second thread drive housing fixedly mounted intermediatelyof the other of said channel means and having a rotating nut drivemember engaging the threads of said second screw rod; drive means ineach of said housing for rotating its drive nut member; a rigid crossshaft interconnecting said drive means of said housings for simultaneousrotation thereof; an electric drive motor drivingly connected to saidcross shaft where said dolly means can be simultaneously advanced andretracted relative to their respective pivot fixtures; a pair ofvertically oriented scissor-type lift arms, one of said pair connectedbetween one of said dolly means and its pivot fixture and the other ofsaid pair connected between the other of said dolly means and its pivotfixture whereby a work platform connected to said pair of verticallyoriented lift arms is raised and lowered as said dolly means aresimultaneously reciprocated in their associated channel means.
 10. Themobile scaffolding machine as defined in claim 9 wherein a compressionspring is coaxially mounted between each threaded drive housing and theend of its screw rod extending therefrom toward its associated pivotfixture whereby said compression spring will be compressed as itsassociated dolly moves away from its pivot fixture.
 11. The mobilescaffolding machine of claim 10 wherein said compression springs areoperative only to bias their associated screw rods when saidscissor-type lift arms are between their most retracted position and apartially extended position having said arms at an angle no greater thanabout 45 degrees to the horizontal and to urge extension of said liftarms from their retracted position to said partially extended positionwhereby the force stored in said compression springs by retraction ofsaid lift arms is available for supplementing the force of said motorthrough the positions of said lift arms having the most disadvantageouslever moments to said screw rods.
 12. The mobile scaffolding machine asdefined in claim 9 wherein the electric drive motor is a variable speeddrive motor so the speed of simultaneous movement of said dolly means intheir associated channels can be controlled.
 13. The mobile scaffoldingmachine defined in claim 12 wherein the electric drive motor is a DCdrive motor and its speed is controlled with a control circuit employinga SCR operable to pulse the drive motor at different frequencies toselectively change its speed.
 14. The mobile scaffolding machine definedin claim 13 wherein a control circuit is provided to change the pulserate of the SCR, said control circuit having a manually operated devicefor chAnging the pulse rate of the SCR circuit.
 15. The mobilescaffolding machine defined in claim 14 wherein the manually controlleddevice includes a lever means which includes a reversing switch and apotentiometer whereby advancing the lever from a neutral position in onedirection will cause the motor to drive clockwise at a rate proportionalto the displacement of said lever from a neutral position and theadvance of said lever from said neutral position in the other directionwill cause said motor to rotate in a counter-clockwise mannerproportional to the distance said lever is moved from said neutralposition.
 16. The mobile scaffolding machine as defined in claim 15wherein the lever means is mounted on the work platform whereby theascent and descent of the platform can be controlled directly therefrom.17. The mobile scaffolding machine as defined in claim 15 wherein therectangular mobile base with dirigible wheels includes an electric drivemotor and the control circuit can be switched so the lever means can beutilized to control the movement of said mobile base in speed anddirection.